The present invention relates to the handling of wind turbine blades aboard a vessel, in particular an installation vessel for wind turbines, especially offshore wind turbines.
Long-distance shipping of wind turbine blades typically involves arranging the blades longitudinally inside the hull or transport compartment of a ship. For the purposes of installing wind turbines, especially offshore wind turbines, the main wind turbine elements such as tower, nacelle and blades or rotors are typically loaded aboard an installation vessel equipped with ancillary equipment for turbine erection. Installation vessels typically resemble a floating work platform more than a traditional transport ship. These vessels are generally loaded with turbine elements at a coastal location local to the planned turbine erection site.
Wind turbine blades may be transported aboard vessels such as installation vessels by placing them in racks on a loading surface such as a deck. The blades are typically loaded onto and unloaded from such vessels in a horizontal orientation of the blades. This is because lifting equipment for loading or unloading is typically configured for horizontal handling of the blades. The dimensions of installation vessels are typically such that the blades may extend to some extent beyond side of such vessels. This creates a hazard in the form of a risk of blade dipping in agitated waters or in case the vessel would encounter swell.
One previously suggested rack arrangement for blade stowage aboard a vessel has a capacity for carrying eighteen blades and comprises a fixed root rack and a facing fixed tip rack. Each tip and root rack comprises a set of fixed blade frame portions such that each blade rests substantially horizontally between a pair of blade frame portions effectively comprising a root frame and a corresponding tip frame. Each root or tip rack comprises six side-by-side columns of three blade frames per column. Rows of six frames are arranged in a vertical arrangement with an offset in the longitudinal blade direction at the root rack such that each root frame saddle is vertically clear of the one beneath it. Each tip frame strop can be disengaged from its tip frame to allow loading or unloading of a blade in a lower frame pair. This arrangement allows successive blades to be loaded into in a respective root frame saddle and a corresponding tip frame strop. The blades may thus be placed successively into the fixed frame pairs which make up the rack arrangement. In order to prevent damage arising as a consequence of blades dipping in the water during occasional rolling of an installation vessel, each root and tip rack includes a lower spacer frame fixed to a vessel deck and carrying the respective root or tip rack. This spacer frame ensures a minimum clearance between the stowed blades and the vessel deck, and hence, a minimum clearance between the blades and the water along that portion of the blades which overhangs the side of the transport vessel. This spacer frame arrangement reduces the blade dipping hazard in connection with vessel roll during agitated or rough conditions. A similar rack arrangement including nine pairs of fixed blade frames has also been proposed.
Developments in wind turbine technology have led to ever increasing blade lengths. In order to mitigate for the hazard of blade dipping, the height and overall size of spacer frames has had to increase in order to maintain an appropriate clearance between blade tips and water surface in case of vessel roll. This is very costly in terms of construction material and it wastes already limited space on board the vessel.
The present invention aims to improve blade handling aboard a vessel. In particular, the present invention seeks to improve blade handling and stowage aboard a transport or installation vessel.